geoscenario introduction: yellowstone hotspot · (1908–1993) came up with a theory for these...

Yellowstone is one of America’s most beloved national parks . Did you know that its unique scenery is the result of the area’s geology?

Geoscenario Introduction: Yellowstone Hotspot

Yellowstone National Park lies in a volcanic

caldera, an area that collapsed after an

eruption . Below the caldera is a hotspot .

There, huge amounts of magma sit just below

Earth’s surface . In this geoscenario, you’ll

learn some of the geologic secrets that make

Yellowstone such a special place .

Hydrothermal Features Hot springs are naturally warm bodies of

water . Hot magma heats water underground

to near boiling . Some organisms still manage

to live in these springs .

Its vivid colors and huge size make Grand Prismatic Spring the most photographed feature at Yellowstone. Extremely hot water rises 37 m from a crack in Earth’s crust to form this hot spring.

109Investigation 8: Geoscenarios

1558514_MSNG_Earth History_Text.indd 109 11/29/18 3:15 PM

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Under the Yellowstone Hotspot

The water in mud pots tends to be acidic .

It dissolves the surrounding rock . Hot water

mixes with the dissolved rock to create

bubbly pots .

Other hydrothermal features include

fumaroles and geysers . Fumaroles

are cracks that allow steam to escape

continuously . Geysers are hot springs that

trap steam underground . As pressure builds,

the steam erupts . Yellowstone has more than

300 geysers, more than any other place in

the world . Yellowstone’s most famous geyser

is Old Faithful . While it is neither the largest

nor the most regular geyser, it is certainly the

most watched .

Hotspot TheoryMost earthquakes and volcanic eruptions

occur near plate boundaries, but there are

some exceptions . In 1963, John Tuzo Wilson

(1908–1993) came up with a theory for these

exceptions . He described stationary magma

chambers beneath the crust . These hotspots

can cause volcanic activity far from any

plate boundary .

Recent technology has allowed scientists

to create a picture of the magma chamber

under the Yellowstone Hotspot . The chamber

is huge . It sits underneath parts of Montana,

Wyoming, and Idaho .

Unlike a hot spring, a geyser periodically shoots heated groundwater and steam up into the air. Yellowstone’s Old Faithful geyser is world famous.

Caldera

North–South(kilometers) West–East

(kilometers)

MontanaWyoming

Idaho

Dep

th (k

ilom

eter

s)

North

Yellowstone

240160

800

-80-160

-240

240160800-80-160-240

640

480

320

160

0

Seismologists at the University of Utah and the US Geological Survey mapped the location of this magma chamber, which sits under three US states and Yellowstone National Park. The caldera, or crater-like depression, from the last eruption (640,000 years ago) is outlined in red.

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Path of Hawaiian Hotspot

Understanding the Path of Hotspots

Hotspots appear to move over time .

Evidence indicates, however, that what moves

is a tectonic plate . Wilson suggested that the

Pacific Plate moved northward over the fixed

Hawaiian Hotspot . The island of Hawaii is the

youngest and most volcanically active island .

The other Hawaiian islands get older and less

active as you move north .

Likewise, the North American Plate has been

moving over the fixed Yellowstone Hotspot .

The hotspot is melting a path through the

Rocky Mountains .

SupereruptionsThe past three eruptions from Yellowstone

have been supereruptions . The Lava Creek

eruption, 640,000 years ago, was one of the

largest in history . It covered large areas with

thick ash, as shown on the map on the

next page .

As the Pacific Plate has slowly moved north over a hotspot, the volcanic island chain of Hawaii has formed. Magma breaking through the crust at the hotspot is currently building the Big Island.

PACIFIC PLATE

Hawaiian Ridge

Hotspot(magmachamber)

Kauai

Oahu

Maui

Hawaii

111Investigation 8: Geoscenarios


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Take a moment to consider the volume

of some major eruptions . Mount St . Helens

erupted in 1980 and ejected about 1 cubic

kilometer (km3) of volcanic material . How

does that compare to Yellowstone? When the

hotspot erupted 640,000 years ago, it ejected

over 1,000 km3 of volcanic materials . When

it erupted 2 .1 million years ago, it ejected an

astonishing 25,000 km3 of ash and debris .

Ash covered much of what is now the United

States .

The magma chamber below Yellowstone

may cause another supereruption in the

future . Geologists monitor the area carefully

for signs of geologic activity . They hope to

predict future eruptions and help keep people

safe .

Geothermal energy useWater heated underground that comes

to the surface makes geothermal (heat

from Earth) energy available to humans .

Geothermal energy from geysers can be used

to produce electricity . This is a renewable

energy source, because it is constantly

replenished . Should the geothermal energy

in Yellowstone and the surrounding areas be

used to produce electric power? Scientists and

engineers are conducting studies to explore

this . The studies consider the impact electric

generation would have on the national park .

Huckleberry Ridge ash

bed

Mesa Falls ash bed

Lava Creek ash bed

MountSt Helens

MountSt Helensash 1980

LongValley

Caldera

Bishopash bed

YellowstonePlateau

400 MILES

400 KILOMETERS

0

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Geologists compare remnants of ash beds from ancient eruptions to ash beds of recent eruptions. They can infer the size of ancient, massive volcanic events from these comparisons.

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geoscenario introduction: yellowstone hotspot · (1908–1993) came up with a theory for these...

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